Blockade of Dickkopf (DKK)-1 induces fusion of sacroiliac joints

Serum biomarkers and their relationship to axial spondyloarthritis associated with inflammatory bowel diseases

Spondyloarthritis (SpA) constitute a group of chronic inflammatory immune-mediated rheumatic diseases characterized by genetic, clinical, and radiological features. Recent efforts have concentrated on identifying biomarkers linked to axial SpA associated with inflammatory bowel disease (IBD), offering predictive insights into disease onset, activity, and progression. Genetically, the significance of the HLA-B27 antigen is notably diminished in ankylosing spondylitis (AS) associated with IBD, but is heightened in concurrent sacroiliitis. Similarly, certain polymorphisms of endoplasmic reticulum aminopeptidase (ERAP-1) appear to be involved. Carriage of variant NOD2/CARD15 polymorphisms has been demonstrated to correlate with the risk of subclinical intestinal inflammation in AS. Biomarkers indicative of pro-inflammatory activity, including C-reactive protein (CRP) along with erythrocyte sedimentation rate (ESR), are among the consistent predictive biomarkers of disease progression. Nevertheless, these markers are not without limitations and exhibit relatively low sensitivity. Other promising markers encompass IL-6, serum calprotectin (s-CLP), serum amyloid (SAA), as well as biomarkers regulating bone formation such as metalloproteinase-3 (MMP-3) and Dickkopf-related protein 1 (DKK-1). Additional candidate indicators of structural changes in SpA patients include matrix metalloproteinase-3 (MMP-3), vascular endothelial growth factor (VEGF), tenascin C (TNC), and CD74 IgG. Fecal caprotein (f-CLP) levels over long-term follow-up of AS patients have demonstrated predictive value in anticipating the development of IBD. Serologic antibodies characteristic of IBD (ASCA, ANCA) have also been compared; however, results exhibit variability. In this review, we will focus on biomarkers associated with both axial SpA and idiopathic intestinal inflammation, notably enteropathic spondyloarthritis.

The sacroiliac joint: An original and highly sensitive tool to highlight altered bone phenotype in murine models of skeletal disorders

Bone disorders may affect the skeleton in different ways, some bones being very impaired and others less severely. In translational studies using murine models of human skeletal diseases, the bone phenotype is mainly evaluated at the distal femur or proximal tibia. The sacroiliac joint (SIJ), which connects the spine to the pelvis, is involved in the balanced transfer of mechanical energy from the lumbar spine to the lower extremities. Because of its role in biomechanical stress, the SIJ is a region of particular interest in various bone diseases. Here we aimed to characterize the SIJ in several murine models to develop a highly reliable tool for studying skeletal disorders. We performed a 12-month in vivo micro-computed tomography (micro-CT) follow-up to characterize the SIJ in wild-type (WT) C57BL/J6 mice and compared the bone microarchitecture of the SIJ and the distal femur at 3 months by micro-CT and histology. To test the sensitivity of our methodology, the SIJ and distal femur were evaluated at 3 and 6 months, in 2 murine models of skeletal disorder, X-linked hypophosphatemia (Hyp mice) and HLA-B27 transgenic mice and compared to WT mice. A multimodal analysis was performed, using a combination of microCT and histological analysis. With the Hyp model, the SIJ displayed more bone microarchitecture alterations than the distal femur. Hyp mice showed a significant reduction in trabecular bone at both the distal femur and sacral slope as compared with WT mice, with a significant positive correlation between trabecular bone parameters of the distal femur and sacral side of the SIJ. Furthermore, trabecular bone parameters (Bone Volume/Total Volume (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N), trabecular pattern factor (Tb.Pf)) were significantly increased compared to femoral parameters at the SIJ. The sacral articular cortical bone, which is indicative of osteoarticular lesions, was altered in Hyp mice. Interestingly, in accordance to previous studies, HLA-B27 transgenic mice did not show any osteoarticular lesions as compared with WT mice. Cortical bone parameters (thickness, porosity), as well as scoring performed with double blinding, did not show difference between the 2 genotypes. The characterization and evaluation of the SIJ surface appears very sensitive to emphasize alterations of bone and joint. The SIJ may represent a valuable tool to investigate both bone and local osteoarticular alterations in murine models of skeletal disorders and might be a relevant site for assessing the response to treatment of chronic bone diseases.

Serum concentration of dickkopf-related protein 1 (DKK1) in psoriatic arthritis in the context of bone remodelling

Psoriatic arthritis (PsA) is a chronic inflammatory disease, characterised by the pathological occurrence of two opposite phenomena-osteoresorption and osteogenesis. Dickkopf-related protein 1 (DKK1) which inhibits the Wingless protein (Wnt) signalling pathway has been shown to be a master regulator of bone remodeling in inflammatory rheumatic diseases. However, the exact relationship between DKK1 serum level and bone remodelling is not clear. The goal of this study is to review state-of-the-art knowledge on the association of serum DKK1 with a bone remodelling in PsA. The MEDLINE-PubMed, EMBASE, Scopus, Web of Science and DOAJ databases were searched for appropriate papers. The English terms: 'DKK1', 'Dickkopf-1' 'Dickkopf related protein 1', 'psoriatic arthritis' and 'PsA' were used for search purposes. Eight original articles and two reviews were identified up to August 2023. In four out of 8 discussed studies DKK1 serum level was higher in PsA patients than in healthy controls [Dalbeth, p < 0.01; Diani, p < 0.001; Chung, p < 0.01; Abd el Hamid, p < 0.001)], it was comparable in another (Daousiss, p = 0.430) and was lower in two (Fassio2017, p < 0.05; Fassio2019, p < 0.05). In one study, the comparative groups included patients with axial spondyloarthritis, where DKK1 serum levels were lower in PsA groups [Jadon, peripheral PsA, p = 0.01]. The true relative serum concentration of DKK1 in PsA, as well as its influence on osteogenesis and osteoresorption, is still equivocal. Further studies on this matter with consistent and stringent methodology are warranted.

Osteoimmunology of Spondyloarthritis

The mechanisms underlying the development of bone damage in the context of spondyloarthritis (SpA) are not completely understood. To date, a considerable amount of evidence indicates that several developmental pathways are crucially involved in osteoimmunology. The present review explores the biological mechanisms underlying the relationship between inflammatory dysregulation, structural progression, and osteoporosis in this diverse family of conditions. We summarize the current knowledge of bone biology and balance and the foundations of bone regulation, including bone morphogenetic protein, the Wnt pathway, and Hedgehog signaling, as well as the role of cytokines in the development of bone damage in SpA. Other areas surveyed include the pathobiology of bone damage and systemic bone loss (osteoporosis) in SpA and the effects of pharmacological treatment on focal bone damage. Lastly, we present data relative to a survey of bone metabolic assessment in SpA from Italian bone specialist rheumatology centers. The results confirm that most of the attention to bone health is given to postmenopausal subjects and that the aspect of metabolic bone health may still be underrepresented. In our opinion, it may be the time for a call to action to increase the interest in and focus on the diagnosis and management of SpA.

Updates on ankylosing spondylitis: pathogenesis and therapeutic agents

Ankylosing spondylitis (AS) is an autoinflammatory disease that manifests with the unique feature of enthesitis. Gut microbiota, HLA-B*27, and biomechanical stress mutually influence and interact resulting in setting off a flame of inflammation. In the HLA-B*27 positive group, dysbiosis in the gut environment disrupts the barrier to exogenous bacteria or viruses. Additionally, biomechanical stress induces inflammation through enthesial resident or gut-origin immune cells. On this basis, innate and adaptive immunity can propagate inflammation and lead to chronic disease. Finally, bone homeostasis is regulated by cytokines, by which the inflamed region is substituted into new bone. Agents that block cytokines are constantly being developed to provide diverse therapeutic options for preventing the progression of inflammation. In addition, some antibodies have been shown to distinguish disease selectively, which support the involvement of autoimmune immunity in AS. In this review, we critically analyze the complexity and uniqueness of the pathogenesis with updates on the findings of immunity and provide new information about biologics and biomarkers.

Increased Prevalence of Autoimmune Rheumatologic Diseases in Patients With Primary Hyperparathyroidism

Background Parathyroid hormone (PTH) and Dickkopf-related protein 1 (DKK-1) have been mentioned together at the intersection of autoimmune rheumatologic diseases (ARDs) and osteoimmunology. However, few studies have evaluated the association between primary hyperparathyroidism (PHPT) and ARDs. Methodology This retrospective study included 225 PHPT patients and 386 patients with thyroid nodules as a control group. The electronic hospital records of all patients were screened going back nine years for the presence of ARDs. Patients who were diagnosed at least three months ago, had complete serologic tests, and were continuing with rheumatologic follow-up were included. Results The prevalence of ARDs in the PHPT group was 9.77% (22/225), while the prevalence of ARDs in the CG was 1.04% (4/386, p < 0.001). The prevalence of rheumatoid arthritis in the PHPT group was 4.4% (10/225), ankylosing spondylitis 3.1% (7/225), systemic lupus erythematosus 0.88% (2/225), Behçet's disease 0.88% (2/225), and mixed connective tissue disease 0.44% (1/225). Of the 22 patients with ARDs, 21 (95.45%) were diagnosed before they were diagnosed with PHPT, and the median time from diagnosis with ARD to the onset of PHPT was 36 months (interquartile range = 61.5). Logistic regression analysis showed a positive correlation between the duration of PHPT and ARDs (odds ratio (OR) = 1.06; 95% confidence interval (CI) = 1.02-1.09, p < 0.001) and a negative correlation between ARDs and calcium levels (OR = 0.26; 95% CI = 0.09-0.79, p = 0.018). Conclusions The prevalence of ARDs increased in PHPT patients and PHPT accompanying ARDs developed after rheumatologic disease. ARDs with PHPT are cases with a prolonged duration of PHPT and mildly elevated calcium, probably preceded by parathyroid hyperplasia. Therefore, the factors that cause ARDs may trigger a process that leads to mild PHPT.

DNA methylation of DKK-1 may correlate with pathological bone formation in ankylosing spondylitis

OBJECTIVE

To investigate DNA methylation (DNAm) status of dickkopf-associated protein 1 (DKK-1) in ossified hip capsule synovium and serum among patients with ankylosing spondylitis (AS).

METHODS

Western blot was applied to detect the level of DKK-1 protein expression in hip joint capsule tissues from four patients with AS as well as four patients with femoral neck fracture (FNF) caused by trauma as control. DKK-1 gene promoter methylation (GPM) was examined by methylation-specific polymerase chain reaction. Reverse transcription-polymerase chain reaction was performed to examine the messenger RNA (mRNA) levels of DKK-1, β-catenin, and Wnt3a in both tissue and serum. The DNAm status of serum DKK-1 was measured among 36 patients with AS and syndesmophytes (AS + syndesmophytes group), 40 patients with AS but no syndesmophyte (AS group), and 42 healthy individuals (control group). Also, the serum levels of DKK-1 were measured by enzyme-linked immunosorbent assay. The modified New York criteria (mNYC) together with the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) were adopted to examine the radiographic progression of AS. The receiver operating characteristic (ROC) curve was applied to investigate the diagnostic value of the methylation rate of DKK-1 with regard to radiographic progression.

RESULTS

The expressions of DKK-1 protein and mRNA in hip joint capsule tissues of AS patients were significantly lower, while DKK-1 GPM rate, β-catenin mRNA, and Wnt3a mRNA were markedly higher when compared with FNF group. For serum samples, the DKK-1 methylation rate was significantly higher in AS+ syndesmophytes group in contrast to AS group and healthy controls. Serum levels of DKK-1 protein and mRNA in AS with syndesmophytes group were markedly decreased, while β-catenin mRNA and Wnt3a mRNA expressions were significantly increased than AS with no syndesmophyte group and the healthy control group. AS patients in Grade 4 showed a significantly higher serum DKK-1 GPM rate than those in Grade 3 based on mNYC. Serum DKK-1 GPM level was markedly and positively correlated with mSASSS. Serum levels of DKK-1 in AS+ syndesmophytes group were markedly lower compared with AS but no syndesmophyte group and healthy controls. ROC curve analysis indicated that serum DKK-1 methylation rate serves as a decent indicator for AS radiographic progression.

CONCLUSION

DNAm of DKK-1 may correlate with pathological bone formation in AS, which may provide new strategies for the treatment of AS abnormal bone formation.

Assessment of Circulating lncRNA H19 in Ankylosing Spondylitis Patients and Its Correlation with Disease Activity

Ankylosing spondylitis (AS) is a chronic inflammatory disease that results in severe pain and stiffness in the joints. The causes and pathophysiology of AS are still largely unknown. The lncRNA H19 plays key roles in the pathogenesis of AS by mediating inflammatory progression by acting in the axis of IL-17A/IL-23. The aims of this study were determining the role of lncRNA H19 in AS and assessing its clinical correlation. A case-control study was conducted and qRT-PCR was utilized to measure H19 expression. Comparing AS cases to healthy controls, it was found that H19 expression was significantly upregulated. For AS prediction, H19 demonstrated a 81.1% sensitivity, 100% specificity, and 90.6% diagnostic accuracy at a lncRNA H19 expression value of 1.41. lncRNA H19 had a significantly positive correlation with AS activity, MRI results, and inflammatory markers. lncRNA H19 seemed to be an independent predictor of AS (adjusted OR of 211 (95% CI: 4.7-939; p = 0.025)). After 3 months of clinical follow-up, seventeen patients (32.1%) showed minimal clinical improvement and fifteen patients (28.3%) showed major improvement. AS activity scores were significantly decreased in patients with high H19 expression. A significantly elevated lncRNA H19 expression was observed in AS cases compared with that in healthy controls. These results suggest that upregulation of lncRNA H19 expression may be involved in the pathogenesis of AS. The expression of the lncRNA H19 is related to the duration and activity of the disease. LncRNA H19 expression seems to be an independent predictor of AS.

Chronic arthritides and bone structure: focus on rheumatoid arthritis-an update

Normal bone remodeling depends of a balance between bone forming cells, osteoblasts and bone resorbing cells, the osteoclasts. In chronic arthritides and some inflammatory and autoimmune diseases such as rheumatoid arthritis, there is a great constellation of cytokines produced by pannus that impair bone formation and stimulate bone resorption by inducing osteoclast differentiation and inhibiting osteoblast maturation. Patients with chronic inflammation have multiple causes that lead to low bone mineral density, osteoporosis and a high risk of fracture including circulating cytokines, impaired mobility, chronic administration of glucocorticoids, low vitamin D levels and post-menopausal status in women, among others. Biologic agents and other therapeutic measures to reach prompt remission might ameliorate these deleterious effects. In many cases, bone acting agents need to be added to conventional treatment to reduce the risk of fractures and to preserve articular integrity and independency for daily living activities. A limited number of studies related to fractures in chronic arthritides were published, and future investigation is needed to determine the risk of fractures and the protective effects of different treatments to reduce this risk.

The Increasing Level of DKK-1 as a New Bone Formation Factor in Patients with Early Spondyloarthritis

The role of dickkopf-related protein 1 (DKK-1) in radiographic development may become a robust marker for early spondyloarthritis (SpA) diagnosis. This study aimed at determining the serum DKK-1 profile in patients with SpA and investigating its relationship with SpA progression. Supported by analyzing the BMD data which aims to affirm the potential of DKK-1 as a biomarker for early diagnosis of SpA, this research may become the early study to produce a robust tool to diminish the fatal impacts in SpA. This cross-sectional study included patients with SpA using ASAS 2010 criteria from Dr. Soetomo General Hospital, Indonesia. Collected data included patients' general characteristics, disease duration, disease activity using ASDAS-CRP and ASDAS-ESR, serum DKK-1 levels, and BMD. The patients were classified as early SpA if the disease duration was ≤5 years and established SpA if the disease duration was >5 years, while the low BMD was indicated by Z score ≤ -2.00. The correlation was tested using the Spearman or Pearson test. The differences in patients' characteristics among early and established SpA and also between low and normal BMD were tested using the unpaired T-test or the Mann-Whitney test. The serum DKK-1 levels in early SpA (7365 ± 2067 pg/dL) were significantly higher than those in established SpA (5360 ± 1054 pg/dL). Serum DKK-1 levels were also associated with disease duration (r = -0.370, p = 0.040) and BMD at the total hip (r = 0.467, p = 0.028). The differences in all patients' clinical parameters were not found between patients with low BMD at any site and patients with normal BMD unless in the BMI (p = 0.019). Our findings found DKK-1 as a potential diagnostic marker for early SpA. Early diagnosis may lead to rapid treatment to delay disease progression and prevent future impairment.

Novel insights into the anatomy and histopathology of the sacroiliac joint and correlations with imaging signs of sacroiliitis in case of axial spondyloarthritis

For a better understanding of the pathophysiology of spondyloarthropathy (SpA), a detailed anatomical description of the sacroiliac joint is required because sacroiliitis is the earliest and most common sign of SpA and an essential feature for the diagnosis of ankylosing spondylitis. Beyond the anatomy, the histopathology of sacroiliac entheses and immunological mechanisms involved in sacroiliitis are crucial for a better understanding of disease causation. In this narrative review, we discuss the core anatomical, histological, and immunohistological observations involved in the development of sacroiliitis, focusing particularly on imaging-based information associated with sacroiliitis. Finally, we try to answer the question of whether at the sacroiliac joint, enthesitis precedes synovitis and subchondral bone changes in SpA.

Anti-tumor necrosis factor alpha treatment does not influence serum levels of the markers associated with radiographic progression in ankylosing spondylitis

OBJECTIVES

The study aimed to determine the levels of change of the markers related to radiographic progression, such as Dickkopf-1 (DKK-1), sclerostin (SOST), bone morphogenetic protein (BMP)-2 and -4, and interleukin (IL)-17 and -23, in ankylosing spondyloarthritis (AS) during anti-tumor necrosis factor alpha (TNF-α) treatment.

PATIENTS AND METHODS

Fifty-three anti-TNF-α naïve AS patients (34 males, 19 females; median: 38 years; range, 20 to 52 years) refractory to conventional treatments meeting the modified New York criteria or Assessment of SpondyloArthritis International Society classification criteria were enrolled to this cross-sectional, controlled study between October 2015 and January 2017. Fifty healthy volunteers (35 males, 15 females; median: 36 years; range, 18 to 55 years) with similar age and sex characteristics were recruited. Serum DKK-1, BMP-2, BMP-4, SOST, IL-17, and IL-23 levels were measured in both groups. The serum levels of the markers were measured again after about two years (mean follow-up duration of 21.7±6.4 months) in AS patients who started anti-TNF-α treatment. Demographic, clinical characteristics, and laboratory parameters were recorded. The disease activity at the time of inclusion was assessed through the Bath Ankylosing Spondylitis Disease Activity Index.

RESULTS

Serum DKK-1, SOST, IL-17, and IL-23 levels in the AS group before anti-TNF-a treatment were significantly higher compared to the control group (p<0.01 for DKK-1, p<0.001 for others). There was no difference regarding serum BMP-4 levels, whereas BMP-2 levels were significantly higher in the control group (p<0.01). Forty (75.47%) AS patients had serum marker levels measured after anti-TNF-α treatment. No significant change was observed in the serum levels of these 40 patients measured 21.7±6.4 months after the initiation of anti-TNF-α treatment (p>0.05 for all).

CONCLUSION

In AS patients, there was no change in DKK-1/SOST, BMP, and IL-17/23 cascade with anti-TNF-α treatment. This finding may suggest that these pathways act independently of each other, and their local effects are not influenced by systemic inflammation.

How Has Molecular Biology Enhanced Our Undertaking of axSpA and Its Management

PURPOSE

This review aims at investigating pathophysiological mechanisms in spondyloarthritis (SpA). Analysis of genetic factors, immunological pathways, and abnormalities of bone metabolism lay the foundations for a better understanding of development of the axial clinical manifestations in patients, allowing physician to choose the most appropriate therapeutic strategy in a more targeted manner.

RECENT FINDINGS

In addition to the contribution of MHC system, findings emerged about the role of non-HLA genes (as ERAP1 and 2, whose inhibition could represent a new therapeutic approach) and of epigenetic mechanisms that regulate the expression of genes involved in SpA pathogenesis. Increasing evidence of bone metabolism abnormalities secondary to the activation of immunological pathways suggests the development of various bone anomalies that are present in axSpA patients. SpA are a group of inflammatory diseases with a multifactorial origin, whose pathogenesis is linked to the genetic predisposition, the action of environmental risk factors, and the activation of immune response. It is now well known how bone metabolism leads to long-term structural damage via increased bone turnover, bone loss and osteoporosis, osteitis, erosions, osteosclerosis, and osteoproliferation. These effects can exist in the same patient over time or even simultaneously. Evidence suggests a cross relationship among innate immunity, autoimmunity, and bone remodeling in SpA, making treatment approach a challenge for rheumatologists. Specifically, treatment targets are consistently increasing as new drugs are upcoming. Both biological and targeted synthetic drugs are promising in terms of their efficacy and safety profile in patients affected by SpA.

Dickkopf-1 directs periosteal bone formation in two murine models of inflammatory arthritis

OBJECTIVE

The Wnt signalling antagonist Dickkopf-1 (DKK1) inhibits osteoblast differentiation and function and has been described to play a central role in promoting bone loss, while blockade of DKK1 increases bone formation. We investigated the effects of DKK1 on periosteal new bone formation in two murine models of inflammatory arthritis, the antigen-induced arthritis (AIA) and K/BxN serum transfer arthritis (STA) models.

METHOD

The flare variant of AIA was induced in wild-type mice and a blocking antibody to DKK1, control rat immunoglobulin G (IgG), or phosphate-buffered saline (PBS) was administered starting on day 14, a time at which inflammation and erosions are known to be established. Knees were assessed for histological inflammation and periosteal new bone formation was quantitated. In addition, STA was generated in transgenic (Tg) mice with osteoblast-specific overexpression of Dkk1 and littermate controls. New bone formation around the wrists of these mice was quantified by micro-computed tomography.

RESULTS

Blockade of DKK1 in arthritic mice resulted in significantly more periosteal new bone formation compared to mice treated with control rat IgG or PBS. Conversely, in the setting of increased Dkk1 expression, arthritic Dkk1 Tg mice developed significantly less periosteal new bone than arthritic controls.

CONCLUSION

DKK1 is a regulator of periosteal bone formation in inflammatory arthritis. Thus, regulation of DKK1 may be considered as a therapeutic approach in inflammatory diseases in which patients suffer from excessive periosteal bone formation, such as spondyloarthritis.

DKK-1 Is Underexpressed in Mesenchymal Stem Cells from Patients with Ankylosing Spondylitis and Further Downregulated by IL-17

Dickkopf-1 (Dkk-1) is a key regulator of bone remodeling in spondyloarthropathies. Nevertheless, data regarding its expression in cells of pathophysiologic relevance, such as mesenchymal stem cells (MSCs), are lacking. Herein, we aimed to address DKK1 gene expression and Wnt pathway activation in MSCs from patients with ankylosing spondylitis (AS) and explore the effect of IL-17 on MSCs with respect to DKK-1 expression and Wnt pathway activation. Primary MSCs were isolated from the bone marrow of the femoral head of two patients with AS and two healthy controls undergoing orthopedic surgery. MSCs were cultured for 7 days in expansion medium and for 21 days in osteogenic medium in the presence or absence of IL-17A. Gene expression of DKK-1 and osteoblastic markers was determined by RT-PCR. Alkaline phosphatase activity, alizarin red and Van Kossa staining were used to assess osteoblastic function and mineralization capacity. DKK-1 was significantly downregulated in MSCs and osteoblasts from patients with AS compared to controls. Moreover, MSCs and osteoblasts from AS patients displayed increased Wnt pathway activation and enhanced osteoblastic activity, as indicated by increased expression of osteoblast marker genes and alkaline phosphatase activity. IL-17 downregulated DKK-1 expression and increased osteoblastic activity and mineralization capacity. DKK-1 is underexpressed in MSCs from AS patients compared to controls, whereas IL-17 has an inhibitory effect on DKK-1 expression and stimulates osteoblastic function. These data may have pathogenetic and clinical implications in AS.

Drug Discovery of DKK1 Inhibitors

Dickkopf-1 (DKK1) is a well-characterized Wnt inhibitor and component of the Wnt/β-catenin signaling pathway, whose dysregulation is associated with multiple abnormal pathologies including osteoporosis, Alzheimer's disease, diabetes, and various cancers. The Wnt signaling pathway has fundamental roles in cell fate determination, cell proliferation, and survival; thus, its mis-regulation can lead to disease. Although DKK1 is involved in other signaling pathways, including the β-catenin-independent Wnt pathway and the DKK1/CKAP4 pathway, the inhibition of DKK1 to propagate Wnt/β-catenin signals has been validated as an effective way to treat related diseases. In fact, strategies for developing DKK1 inhibitors have produced encouraging clinical results in different pathological models, and many publications provide detailed information about these inhibitors, which include small molecules, antibodies, and nucleic acids, and may function at the protein or mRNA level. However, no systematic review has yet provided an overview of the various aspects of their development and prospects. Therefore, we review the DKK1 inhibitors currently available or under study and provide an outlook on future studies involving DKK1 and drug discovery.

Bone Involvement in Patients with Spondyloarthropathies

Spondyloarthropathies (SpA) are common systemic inflammatory rheumatic diseases, in which, as in other rheumatic diseases, levels of markers of bone resorption are elevated, leading to bone loss and elevated risk of vertebral fractures. However, the diseases are also associated with new bone formation in the spine, the so-called syndesmophytes. We tried to unravel the pathogenesis of formation and growth of syndesmophytes and evaluated new diagnostic and treatment options. After a successful meeting of the Working Group on Rheumatic Diseases at the ECTS 2020, we (WL and CR) were excited about the quality of the speakers (CM, JH, AG, and GL) and their complimentary lectures. Given the relative lack of reviews on spondyloarthropathies and bone, we decided to work together on a comprehensive review that might be interesting for basic scientists and clinically relevant for clinicians. Radiographic progression in axSpA is linked to several risk factors, like male sex, smoking, HLA-B-27, increased levels of CRP, presence of syndesmophytes, and marked inflammation on MRI. The potential role of mechanical stress in the context of physically demanding jobs has been also suggested to promote structural damages. Different treatment options from NSAIDs to biologic agents like TNF inhibitors (TNFi) or IL-17inhibitors (IL-17i) result in a reduction of inflammation and symptoms. However, all these different treatment options failed to show clear and reproducible results on inhibition on syndesmophyte formation. The majority of data are available on TNFi, and some studies suggested an effect in subgroups of patients with ankylosing spondylitis. Less information is available on NSAIDs and IL-17i. Since IL-17i have been introduced quite recently, more studies are expected. IL-17 inhibitors (Il-17i) potently reduce signs and symptoms, but serum level of IL-17 is not elevated, therefore, IL-17 probably has mainly a local effect. The failure of anti-IL-23 in axSpA suggests that IL-17A production could be independent from IL-23. It may be upregulated by TNFα, resulting in lower expression of DKK1 and RANKL and an increase in osteogenesis. In active AS markers of bone resorption are increased, while bone formation markers can be increased or decreased. Bone Turnover markers and additional markers related to Wnt such as DKK1, sclerostin, and RANKL are valuable for elucidating bone metabolism on a group level and they are not (yet) able to predict individual patient outcomes. The gold standard for detection of structural lesions in clinical practice is the use of conventional radiographics. However, the resolution is low compared to the change over time and the interval for detecting changes are 2 years or more. Modern techniques offer substantial advantages such as the early detection of bone marrow edema with MRI, the fivefold increased detection rate of new or growing syndesmophytes with low-dose CT, and the decrease in 18F-fluoride uptake during treatment with TNFα-inhibitors (TNFi) in a pilot study in 12 AS patients. Detection of bone involvement by new techniques, such as low-dose CT, MRI and 18-Fluoride PET-scans, and bone turnover markers, in combination with focusing on high-risk groups such as patients with early disease, elevated CRP, syndesmophytes at baseline, male patients and patients with HLA-B27 + are promising options for the near future. However, for optimal prevention of formation of syndesmophytes we need more detailed insight in the pathogenesis of bone formation in axSpA and probably more targeted therapies.

Regulation of bone mass in inflammatory diseases

Inflammation is among the major determinants of bone loss in chronic disease and aging. Bone metabolism is radically affected by inflammation with consequent bone loss and increased fracture risk. Various cytokines and mediators are involved in the pathogenesis of bone loss in inflammatory conditions. The present review has the aim of discussing the main pathways involved in the pathogenesis of bone loss in inflammatory diseases, focusing in particular on the Wnt system and its regulators. Literature review of studies published between inception to 2021 on osteoporosis and inflammation was conducted. I will discuss the epidemiology of osteoporosis and fractures in common inflammatory diseases. The molecular basis of bone loss related to inflammation will be discussed as well. Finally, the effects of various anti-inflammatory medications on bone metabolism will be reviewed.

Serum Dickkopf-1 as a potential prognostic marker in patients with rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is a disease of an autoimmune nature that involves all types of joints structures and manifested by chronic joints inflammations and thus their erosions and damage. Dickkopf-1 (DKK-1) is a molecule that has an inhibitory regulation of wingless/integrated genes (Wnt) pathway and has a major role in models of animals with arthritis or joint destruction. Increased DKK-1 levels are implicated in higher resorption of the bone in cases of rheumatoid arthritis and thus with higher probability for joint deformities, while low levels associated with formation of new bone by osteoblasts, we aimed to study the prognostic role of circulating Dickkopf-1 in rheumatoid arthritis.

Results

The present study revealed that the DKK-1 levels were significantly increased in RA patients in relation to the control group (P=0.001). We found a significant positive correlation between DKK-1 level and ESR (P=0.001), Disease Activity Score (DAS 28) (P=0.001), the disease duration (P=0.001), and the presence of bone erosions in plain X-ray of hands (P =0.001). Moreover, we revealed that, at cutoff value 2150, the DKK-1 in RA has 90% sensitivity and 85% specificity.

Conclusions

DKK-l serum level can be used as a potential prognostic biomarker for monitoring of joint erosions and destruction in RA patients. Furthermore, it could be a possible target molecule in the future therapy to control the process of joint destruction.

The TNF-NF-kB-DKK1 Axis Promoted Bone Formation in the Enthesis of Ankylosing Spondylitis

Objective

This study aimed to determine the serum Dickkopf 1 (DKK1) levels in ankylosing spondylitis (AS) patients and decipher the mechanism of tumor necrosis factor (TNF)-mediated DKK1 regulation in human AS enthesis cells.

Methods

The sera were obtained from 103 patients with AS and 30 healthy controls (HCs) The enthesis of facet joints were obtained from 4 AS patients and 5 controls The serum levels of DKK1 were measured using ELISA and compared between AS and HCs The impact of TNF on DKK1 expression in human primary spinal enthesis cells was evaluated using various molecular biology techniques and bone formation indicators.

Results

AS patients showed higher serum DKK1 levels than HCs after adjusting for age (9174 [6153∼1,3100] pg/mL vs 8262 [6703∼9278] pg/mL, p=0043) TNF treatment promoted bone formation and DKK1 expression in both control enthesis cells and those of AS This enhanced bone formation by TNF was pronounced in AS-enthesis than those of controls Mechanically, TNF induced NF-kB activation upregulates the DKK1 transcript level While, NF-kB inhibitor led to downregulate DKK1 expression in the enthesis Besides, DKK1 overexpression promoted bone formation in enthesis.

Conclusion

TNF induced DKK1 expression in the enthesis through NF-kB activation TNF-induced DKK1 expression may play a bone formation in the radiologic progression of ankylosing spondylitis.

Complexity of enthesitis and new bone formation in ankylosing spondylitis: current understanding of the immunopathology and therapeutic approaches

Despite increasing availability of treatments for spondyloarthritis (SpA) including tumour necrosis factor (TNF) and interleukin-17 (IL-17) inhibitors, there is no established treatment that abates new bone formation (NBF) in ankylosing spondylitis (AS), a subset of SpA. Recent research on TNF has revealed the increased level of transmembrane TNF in the joint tissue of SpA patients compared to that of rheumatoid arthritis patients, which appears to facilitate TNF-driven osteo-proliferative changes in AS. In addition, there is considerable interest in the central role of IL-23/IL-17 axis in type 3 immunity and the therapeutic potential of blocking this axis to ameliorate enthesitis and NBF in AS. AS immunopathology involves a variety of immune cells, including both innate and adoptive immune cells, to orchestrate the immune response driving type 3 immunity. In response to external stimuli of inflammatory cytokines, local osteo-chondral progenitor cells activate intra-cellular anabolic molecules and signals involving hedgehog, bone morphogenetic proteins, receptor activator of nuclear factor kappa-B ligand, and Wnt pathways to promote NBF in AS. Here, we provide an overview of the current immunopathology and future directions for the treatment of enthesitis and NBF associated with AS.

Genetics, Epigenetics, and Gender Impact in Axial-Spondyloarthritis Susceptibility: An Update on Genetic Polymorphisms and Their Sex Related Associations

Spondyloarthritis (SpA) is a group of chronic inflammatory rheumatic disease that can be divided into predominantly axial or predominantly peripheral involvement, with or without associated psoriasis, inflammatory bowel disease or previous infection. Axial SpA (axSpA) encompasses ankylosing spondylitis (AS) with radiological sacroiliitis, and a type without radiographic sacroiliitis, called “non-radiographic axial SpA” (nr-axSpA). Males and females show large differences in their susceptibility to SpA, such as distinctions in clinical patterns, phenotypes and in therapeutical response, particularly to TNF inhibitors (TNFi). Several studies indicate that AS women have doubled risk to failure TNFi compared with males. This diversity in drugs’ efficacy among women and men may be caused by differences in the balance of sex hormones and in gene-specific expression likely triggered by X-chromosome instability and gene-specific epigenetic modifications. Evidence reported that polymorphisms in microRNAs on X- and other chromosomes, such as miR-146a, miR-155, miR-125a-5p, miR-151a-3p and miR-22-3p, miR-199a-5p could be involved in the different clinical presentation of SpA, as well as disease activity. In addition, association with non−response to TNFi treatment and presence of IRAK3 and CHUCK genes in SpA patients was recently detected. Finally, polymorphisms in genes involved in IL-23/IL-17 pathway, such as in drug pharmacodynamics and pharmacokinetics may have a role in response to TNFi, IL17i, and IL23i. A major understanding of genomic variability could help in the development of new therapeutic targets or in taking advantages of different mechanisms of action of biological drugs. Moving from the multifactorial etiology of disease, the present review aims at evaluating genetic and epigenetic factors and their relationship with sex and bDMARDs response, helping to investigate the different expression among males and females of genes on X- and other chromosomes, as well as mi-RNA, to highlight relationships between sex and occurrence of specific phenotypes and symptoms of the disease. Moreover, the role of the epigenetic modification in relation to immune-regulatory mechanisms will be evaluated.

Tail suspension delays ectopic ossification in proteoglycan-induced ankylosing spondylitis in mice via miR-103/DKK1

Ankylosing spondylitis (AS), characterized by inflammatory lesions and osteophyte formation, is a common immune rheumatic disease affecting the sacroiliac and axial joints. A high-intensity mechanical load is known to accelerate the heterotopic ossification associated with enthesitis in AS. Thus, the present study explored whether decreased mechanical load could delay the heterotopic ossification in AS. First, 24-week-old female BALB/c mice were induced with proteoglycan (PG) to establish an AS model. The AS-induced pathological and bone morphological changes of the sacroiliac joint were confirmed by hematoxylin and eosin staining and microCT analysis, respectively. Subsequently, the mice were treated with interventions of different mechanical loads. Using reverse transcription-quantitative PCR, it was revealed that expression levels of the osteogenesis-related genes bone morphogenetic protein-2, runt-related transcription factor 2 and osteocalcin were significantly reduced in sacroiliac bone tissue after intervention with a reduced mechanical load. The level of mechanosensory microRNA (miR)-103 increased in response to reduced mechanical loads. Consistently, in groups with reduced mechanical load, proteins with mechanical functions, including ρ-associated coiled-coil-containing protein kinase 1 (ROCK1), phosphorylated (p)-Erk1/2 and β-catenin, were reduced compared with the PG control. A dual-luciferase assay verified that miR-103 binds to the 3'-untranslated region end of Rock1 mRNA, thus negatively regulating the activity of Rock1 and affecting pathological ossification during AS. However, immunohistochemical staining indicated that the expression of dickkopf Wnt signaling pathway inhibitor 1, an inhibitor of the Wnt/β-catenin pathway, was increased in sacroiliac tissues. The results indicated that tail suspension decreased the mechanical load, thus reducing the bone formation in AS mice. Furthermore, tail suspension could inhibit the activation of mechanical kinase ROCK1 and p-Erk1/2 in the MAPK signaling pathway by upregulating miR-103, thereby inhibiting the classical osteogenesis-related Wnt/β-catenin pathway in AS. In summary, the present study uncovered the ameliorative effect of suspension on AS and its therapeutic potential for AS.

Juvenile Spondyloarthritis: What More Do We Know About HLA-B27, Enthesitis, and New Bone Formation?

Juvenile spondyloarthritis (JSpA) refers to a diverse spectrum of immune-mediated inflammatory arthritides whose onset occurs in late childhood and adolescence. Like its adult counterpart, JSpA is typified by a strong association with human leukocyte antigen-B27 (HLA-B27) and potential axial involvement, while lacking rheumatoid factor (RF) and distinguishing autoantibodies. A characteristic manifestation of JSpA is enthesitis (inflammation of insertion sites of tendons, ligaments, joint capsules or fascia to bone), which is commonly accompanied by bone resorption and new bone formation at affected sites. In this Review, advances in the role of HLA-B27, enthesitis and its associated osteoproliferation in JSpA pathophysiology and treatment options will be discussed. A deeper appreciation of how these elements contribute to the JSpA disease mechanism will better inform diagnosis, prognosis and therapy, which in turn translates to an improved quality of life for patients.

Tenascin-C-mediated suppression of extracellular matrix adhesion force promotes entheseal new bone formation through activation of Hippo signalling in ankylosing spondylitis

Objectives

The aim of this study was to identify the role of tenascin-C (TNC) in entheseal new bone formation and to explore the underlying molecular mechanism.

Methods

Ligament tissue samples were obtained from patients with ankylosing spondylitis (AS) during surgery. Collagen antibody-induced arthritis and DBA/1 models were established to observe entheseal new bone formation. TNC expression was determined by immunohistochemistry staining. Systemic inhibition or genetic ablation of TNC was performed in animal models. Mechanical properties of extracellular matrix (ECM) were measured by atomic force microscopy. Downstream pathway of TNC was analysed by RNA sequencing and confirmed with pharmacological modulation both in vitro and in vivo. Cellular source of TNC was analysed by single-cell RNA sequencing (scRNA-seq) and confirmed by immunofluorescence staining.

Results

TNC was aberrantly upregulated in ligament and entheseal tissues from patients with AS and animal models. TNC inhibition significantly suppressed entheseal new bone formation. Functional assays revealed that TNC promoted new bone formation by enhancing chondrogenic differentiation during endochondral ossification. Mechanistically, TNC suppressed the adhesion force of ECM, resulting in the activation of downstream Hippo/yes-associated protein signalling, which in turn increased the expression of chondrogenic genes. scRNA-seq and immunofluorescence staining further revealed that TNC was majorly secreted by fibroblast-specific protein-1 (FSP1)+fibroblasts in the entheseal inflammatory microenvironment.

Conclusion

Inflammation-induced aberrant expression of TNC by FSP1+fibroblasts promotes entheseal new bone formation by suppressing ECM adhesion forces and activating Hippo signalling.

The Effects of Sex and Estrogen on Radiographic Progression of Ankylosing Spondylitis in Korean Patients

Objective

Ankylosing spondylitis (AS) is a chronic inflammatory disease with obvious male preponderance Males show more severe radiographic manifestations compared with females This study aimed to evaluate the effects of sex and estrogen on the radiographic progression of AS.

Methods

A total of 101 patients with AS were included in this study All of the radiographs were scored using the modified Stoke AS Spine Score (mSASSS) Serum levels of 17β-estradiol (E2), dickkopf-1 (Dkk1), and leptin were detected by enzyme-linked immunosorbent assay The generalized estimating equations model was used to evaluate factors associated with spinal radiographic progression.

Results

The mean age at disease onset was 273±107 years, and 16 patients (158%) were female In the multivariable analysis, body mass index (β-coefficient=012; p=0047) and levels of Dkk1 (β-coefficient=-011; p<0001), and female (β-coefficient=-140; p=0001) were associated with radiographic progression Among male patients with AS, baseline C-reactive protein (β=011; p=0005) and mSASSS (β=021; p=0030) were also associated with radiographic progression E2 and leptin levels were not significantly related to the radiographic progression.

Conclusion

Although female patients were associated with less radiographic progression in AS, there was no significant relationship between serum estrogen level and radiographic progression Results of current study suggests that genetic factors or other environmental factors associated with female may influence radiographic progression in patients with AS.

Chondrogenesis mediates progression of ankylosing spondylitis through heterotopic ossification

Ankylosing spondylitis (AS) is chronic inflammatory arthritis with a progressive fusion of axial joints. Anti-inflammatory treatments such as anti-TNF-α antibody therapy suppress inflammation but do not effectively halt the progression of spine fusion in AS patients. Here we report that the autoimmune inflammation of AS generates a microenvironment that promotes chondrogenesis in spine ligaments as the process of spine fusion. Chondrocyte differentiation was observed in the ligaments of patients with early-stage AS, and cartilage formation was followed by calcification. Moreover, a large number of giant osteoclasts were found in the inflammatory environment of ligaments and on bony surfaces of calcified cartilage. Resorption activity by these giant osteoclasts generated marrow with high levels of active TGF-β, which induced new bone formation in the ligaments. Notably, no Osterix+ osteoprogenitors were found in osteoclast resorption areas, indicating uncoupled bone resorption and formation. Even at the late and maturation stages, the uncoupled osteoclast resorption in bony interspinous ligament activates TGF-β to induce the progression of ossification in AS patients. Osteoclast resorption of calcified cartilage-initiated ossification in the progression of AS is a similar pathologic process of acquired heterotopic ossification (HO). Our finding of cartilage formation in the ligaments of AS patients revealed that the pathogenesis of spinal fusion is a process of HO and explained why anti-inflammatory treatments do not slow ankylosing once there is new bone formation in spinal soft tissues. Thus, inhibition of HO formation, such as osteoclast activity, cartilage formation, or TGF-β activity could be a potential therapy for AS.

Changes in bone formation regulator biomarkers in early axial spondyloarthritis

OBJECTIVE

The hallmark of advanced axial SpA (axSpA) is spine ankylosis due to excessive ectopic bone formation. This prospective study aimed to describe the changes in serum levels of different regulators [sclerostin, dickkopf-1 (DKK-1)] and markers of bone formation [bone morphogenetic protein 7 (BMP-7)] over 5 years in early axSpA patients and to assess determinants of such changes.

METHODS

The DEvenir des Spondyloarthropathies Indifférenciées Récentes cohort is a prospective, multicentre French study of 708 patients with early (>3 months-<3 years) inflammatory back pain suggestive of axSpA. Serum levels of BMP-7, sclerostin and DKK-1 were assessed at baseline and after 2 and 5 years. Changes in bone formation regulators over time were analysed using mixed linear models.

RESULTS

Serum BMP-7 significantly increased over time, with a median relative change of 223.7% [interquartile range (IQR) 0-10 700 (0.17 pg/ml/month), P < 0.001]. Serum sclerostin significantly increased over time, with a median relative change of 14.8% [IQR -7.9-41.4% (0.001 ng/ml/month), P < 0.001]. Serum DKK-1 did not significantly change over time. Serum BMP-7 increased over time in active disease (Ankylosing Spondylitis Disease Activity Score with CRP ≥1.3, P = 0.01), but the increase was less pronounced with TNF inhibitor (TNFi) use (P < 0.001). No determinant was associated with serum sclerostin change.

CONCLUSION

Serum BMP-7 change over 5 years was related with inflammation; it was increased in active disease, but the increase was low with TNFi use. Serum sclerostin levels significantly increased over time, but to a lesser degree than for serum BMP-7.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/, NCT01648907.

Osteoimmunological insights into the pathogenesis of ankylosing spondylitis

Ankylosing spondylitis (AS) is inflammatory arthritis predominantly affecting the spine, which is involved in the disorders of both immune and skeletal systems. The exact pathogenesis of AS is not fully understood. Osteoimmunology is a new subject of study in inflammatory arthritis, in particular the pathogenic events involved in the cross-regulation of both skeletal and immune systems. In this review, we discuss osteoimmunological and pathological changes of AS in the spine that are characterized by altered osteogenesis and osteolytic bone destruction, accompanied by the changes of the immune system. It was revealed that bone cells like mesenchymal stem cells, osteoblast, and osteoclast in crossing talking with immune cells such as T cells, B cells coregulate to the pathogenesis of AS. Further, an array of cytokines and molecules expressed by both skeletal and immune systems contribute to these complex interplays. Understanding the cellular and molecular mechanisms underlying the pathogenesis of AS will lay a foundation for the exploration of the potential new treatment to AS.

Pelvic Protection Limiting Lower Limb Flail Reduces Mortality

Pelvic blast injury is one of the most severe patterns of injury to be sustained by casualties of explosions. We have previously identified the mechanism of injury in a shock tube-mediated murine model, linking outward flail of the lower limbs to unstable pelvic fractures and vascular injury. As current military pelvic protection does not protect against lower limb flail, in this study we have utilized the same murine model to investigate the potential of novel pelvic protection to reduce injury severity. Fifty cadaveric mice underwent shock-tube blast testing and subsequent injury analysis. Pelvic protection limiting lower limb flail resulted in a reduction of pelvic fracture incidence from both front-on (relative risk (RR) 0.5, 95% confidence intervals (CIs) 0.3-0.9, p < 0.01) and under-body (RR 0.3, 95% CI 0.1-0.8 p < 0.01) blast, with elimination of vascular injury in both groups (p < 0.001). In contrast, pelvic protection, which did not limit flail, had no effect on fracture incidence compared to the control group and was only associated with a minimal reduction in vascular injury (RR 0.6, 95% CI 0.4-1.0, p < 0.05). This study has utilized a novel strategy to provide proof of concept for the use of pelvic protection, which limits limb flail to mitigate the effects of pelvic blast injury.

Bone phenotypes in rheumatology - there is more to bone than just bone

Osteoarthritis, rheumatoid arthritis, psoriatic arthritis, and ankylosing spondylitis, all have one clear common denominator; an altered turnover of bone. However, this may be more complex than a simple change in bone matrix and mineral turnover. While these diseases share a common tissue axis, their manifestations in the area of pathology are highly diverse, ranging from sclerosis to erosion of bone in different regions. The management of these diseases will benefit from a deeper understanding of the local versus systemic effects, the relation to the equilibrium of the bone balance (i.e., bone formation versus bone resorption), and the physiological and pathophysiological phenotypes of the cells involved (e.g., osteoblasts, osteoclasts, osteocytes and chondrocytes). For example, the process of endochondral bone formation in chondrocytes occurs exists during skeletal development and healthy conditions, but also in pathological conditions. This review focuses on the complex molecular and cellular taxonomy of bone in the context of rheumatological diseases that alter bone matrix composition and maintenance, giving rise to different bone turnover phenotypes, and how biomarkers (biochemical markers) can be applied to potentially describe specific bone phenotypic tissue profiles.

S100A4 is elevated in axial spondyloarthritis: a potential link to disease severity

Background

S100A4 is a member of calcium binding S100 protein family well known for its role in cancer progression and metastasis. Nevertheless, S100A4 also serves as a negative regulator of bone formation. Dickkopf-1 (DKK-1), marker of bone remodelling, is also implicated in the process of syndesmophyte formation in ankylosing spondylitis. The aim of our study was to evaluate plasma levels of S100A4 in patients with axial spondyloarthritis and to determine the potential association of S100A4 with disease severity, clinical manifestations and with bone changes in a cross-sectional study.

Methods

Fifty-eight patients with axial spondyloarthritis and 40 healthy controls were studied. Biological samples were analysed for S100A4 and Dickkopf-1. Disease activity was assessed according to the Bath Ankylosing Spondylitis Disease Activity Index. C-reactive protein (CRP) was used as a marker of inflammation. Radiographic damage was assessed using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS).

Results

The plasma levels of S100A4 were significantly higher in patients with axial spondyloarthritis compared to heathy controls (p < 0.0001). The levels of S100A4 were higher in early stages of the disease and lower in patients with the presence of syndesmophytes (p = 0.009). Furthermore, we found weak but significant inverse correlation of plasma S100A4 with the mSASSS (r = − 0.363, p = 0.030). Levels of S100A4 were negatively associated with disease duration (r = − 0.404, p = 0.002) and positively with Dickkopf-1 binding capacity (r = 0.312, p = 0.023).

Conclusions

This is the first study showing elevated circulating levels of S100A4 in patients with axial spondyloarthritis, particularly in early stages of the disease prior to spinal involvement, and its significantly lower levels in patients with syndesmophytes. The role of S100A4 in the pathogenesis of axial spondyloarthritis can be suggested.

Wnt Signaling and Biological Therapy in Rheumatoid Arthritis and Spondyloarthritis

The Wnt signaling pathway plays a key role in several biological processes, such as cellular proliferation and tissue regeneration, and its dysregulation is involved in the pathogenesis of many autoimmune diseases. Several evidences support its role especially in bone complications of rheumatic diseases. In Rheumatoid Arthritis (RA), the Wnt signaling is implicated in systemic and localized bone loss, while available data of its role in Spondyloarthritis (SpA) are conflicting. In the last few decades, the quality of life of rheumatic patients has been dramatically improved by biological therapy, targeting cytokines involved in the pathogenesis of these diseases like tumor necrosis factor (TNF)α, interleukin (IL)-1, IL-6, IL-17. In this review, we reviewed the role of Wnt signaling in RA and SpA, focusing on the effect of biological therapy on this pathway and its possible clinical implications.

miR-17-5p Regulates Heterotopic Ossification by Targeting ANKH in Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized with heterotopic ossification of the axis joints ligaments, resulting in joint disability. MicroRNAs (miRNAs) are regulators of mRNAs that play a crucial role in the AS pathological process. Here, we showed that the level of miR-17-5p was significantly higher in fibroblasts and ligament tissues from AS patients as compared to the non-AS individuals. Knockdown of the miR-17-5p from the fibroblasts derived from AS patients exhibited decreased osteogenic differentiation and ossification. On the other hand, AS patient-derived fibroblasts overexpressing miR-17-5p displayed the increased osteogenesis. Furthermore, inhibition of miR-17-5p ameliorated osteophyte formation, and the sacroiliitis phenotype in AS rats received emulsified collagen. Mechanistically, miR-17-5p regulated osteogenic differentiation by targeting the 3ʹ UTR of ankylosis protein homolog (ANKH). Also, downregulation of miR-17-5p slowed AS progression through regulation of cytokines, such as dickkopf-1 (DKK1) and vascular endothelial growth factor (VEGF). In conclusion, our findings reveal a role of the miR-17-5p-ANKH axis in the regulation of heterotopic ossification, which is essential for therapeutic intervention in heterotopic ossification in AS.

Noncoding RNAs Involved in the Pathogenesis of Ankylosing Spondylitis

Ankylosing spondylitis (AS) is a form of arthritis that can lead to fusion of vertebrae and sacroiliac joints following syndesmophyte formation. The etiology of this painful disease remains poorly defined due to its complex genetic background. There are no commonly accepted methods for early diagnosis of AS, nor are there any effective or efficient clinical treatments. Several noncoding RNAs (ncRNAs) have been linked to AS pathogenesis and inflammation via selective binding of their downstream targets. However, major gaps in knowledge remain to be filled before such findings can be translated into clinical treatments for AS. In this review, we outline recent findings that demonstrate essential roles of ncRNAs in AS mediated via multiple signaling pathways such as the Wnt, transforming growth factor-β/bone morphogenetic protein, inflammatory, T-cell prosurvival, and nuclear factor-κB pathways. The summary of these findings provides insight into the molecular mechanisms by which ncRNAs can be targeted for AS diagnosis and the development of therapeutic drugs against a variety of autoimmune diseases.

Dickkopf1: An immunomodulatory ligand and Wnt antagonist in pathological inflammation

The Wnt signaling pathway plays essential roles in tissue or organ homeostasis by regulating cell proliferation and differentiation. Upon tissue or organ injury, inflammation is coupled with tissue repair and regeneration process. The canonical Wnt signaling transduction pathway is crucial for cell proliferation, cell differentiation, and tissue regeneration. Dickkopf1 (DKK1) is a quintessential Wnt antagonist that inhibits the Wnt-mediated tissue repair process. Recent studies reported increased levels of DKK1 in many diseases such as cancer, infection, and musculoskeletal diseases. In many cases, the role of DKK1 has been identified as a pro-inflammatory ligand and the expression levels are associated with poor disease outcomes. A variety of cell types including platelets, endothelial cells, and cancer cells secrete DKK1 upon stimuli. This puts DKK1 in a unique place to view immune responses from multicellular interactions in tissue injury and repair process. In this review, we discuss recent efforts to address the underlying mechanism regarding the pro-inflammatory role of DKK1 in cancer, bone diseases, and other inflammatory diseases.

Restricting Lower Limb Flail is Key to Preventing Fatal Pelvic Blast Injury

Pelvic vascular injury in the casualty of an explosive insult is a principal risk factor for increased mortality. The mechanism of injury has not previously been investigated in a physical model. In this study, a small-animal model of pelvic blast injury with a shock-tube mediated blast wave was utilised and showed that lower limb flail is necessary for an unstable pelvic fracture with vascular injury to occur. One hundred and seventy-three cadaveric mice underwent shock-tube blast testing and subsequent injury analysis. Increasingly displaced pelvic fractures and an increase in the incidence of pelvic vascular injury were seen with increasing lower limb flail; the 50% risk of vascular injury was 66° of lower limb flail out from the midline (95% confidence intervals 59°–75°). Pre-blast surgical amputation at the hip or knee showed the thigh was essential to result in pelvic displacement whilst the leg was not. These findings, corroborated by clinical data, bring a paradigm shift in our understanding of the mechanism of blast injury. Restriction of lower limb flail in the human, through personal protective equipment, has the potential to mitigate the effects of pelvic blast injury.

Altered expression of microRNAs targeting Dkk-1 in peripheral blood mononuclear cells of patients with ankylosing spondylitis

Introduction

Ankylosing spondylitis (AS) is a chronic inflammatory disease characterised by new bone formation, and Dickkopf homologue 1 (Dkk-1) may contribute to the ankylosis of the sacroiliac joint as a main regulator of the Wingless (Wnt) pathway. Increasing evidence shows that microRNAs targeting Dkk-1 might play a critical role in the pathogenesis of rheumatic diseases. We aim to investigate alterations in expression of miRNAs targeting Dkk-1 in AS patients in this study.

Material and methods

The peripheral blood mononuclear cells (PBMCs) of 20 AS patients and 20 normal controls were collected in our study. Three miRNAs targeting DKK1 including miR-29a, miR-335, and miR-363 were selected and quantitative real-time PCR was used to identify the expression of the three miRNAs in these samples. Correlation analysis was conducted between altered miRNA expression and erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Function Index (BASFI), and mSASSS (modified Stoke Ankylosing Spondylitis Spinal Score).

Results

The expression of miR-29a was significantly higher in AS patients than in healthy controls (p < 0.01), while no significance was observed in the expression of miR-335 and miR-363 between AS patients and healthy controls (p > 0.05). No correlation was observed between miR-29a and ESR, CRP, BASDAI, and BASFI (p > 0.05). The elevated miR-29a expression was correlated with disease duration and mSASSS (p < 0.05).

Conclusions

MiR-29a might be a useful marker in AS new bone formation and contributes to the regulation of Dkk-1 in Wnt signalling.

Update on the epidemiology, risk factors, and disease outcomes of axial spondyloarthritis

Axial spondyloarthritis (axSpA) is the prototype of a class of a rheumatic chronic inflammatory disease named spondyloarthritis (SpA). The prevalence of axSpA ranges between 0.1% and 1.4% globally, hence showing geographic differences that can be explained mostly by the prevalence of the HLA-B27 antigen. However, not many studies have evaluated the incidence of this disease. Inflammation may be initiated in the enthesis as a consequence of the action of IL-23, which can activate resident T cells. The elevated expression of IL-23 has been explained by three hypotheses: the presence of HLA-B27, variations in the gut microbiome and the biomechanical stress at the enthesis. However, the role of IL-23 in this whole context is still unclear. In axSpA, the presence of syndesmophytes at baseline, systemic inflammation, and smoking may promote the spinal radiographic damage in these patients. The most frequent comorbidity in these patients is osteoporosis, which is directly associated with ankylosis and inflammation.

Sclerostin rather than Dickkopf-1 is associated with mSASSS but not with disease activity score in patients with ankylosing spondylitis

OBJECTIVE

To determine the serum levels of Dickkopf-1 (DKK-1) and sclerostin, as well as their correlations with the structural damage assessed by modified stoke ankylosing spondylitis spine score (mSASSS) and the disease activity evaluated by ankylosing spondylitis disease activity score (ASDAS) in patients with ankylosing spondylitis (AS).

METHODS

Eighty-eight AS patients, 26 rheumatoid arthritis (RA) patients, and 26 age- and gender-matched healthy controls (HC) were collected from rheumatic clinic of the Second Affiliated Hospital of Zhejiang University, School of Medicine, between March 2015 and July 2015. Demographic data, parameters of ASDAS, and image evaluations of spine (i.e., mSASSS) were collected. The serum levels of DKK-1 and sclerostin were measured using commercially available ELISA kits.

RESULTS

Both DKK-1 and sclerostin were significantly higher in the AS patients than in the controls (1855 ± 84.58 vs. 1406 ± 99.76 pg/ml and 106 ± 6.75 vs. 62.78 ± 6.39 pmol/l, respectively, P < 0.05). The correlation analysis suggested a negative correlation between serum sclerostin and mSASSS (P = 0.019, r² = 0.062). DKK-1 had a trend of positive correlation with mSASSS, but was not statistically significant (P > 0.05). There was no association between the serum levels of DKK-1 or sclerostin and disease activity assessed by ASDAS (P > 0.05). DKK-1 and sclerostin had a negative correlation (P = 0.013, r² = 0.07).

CONCLUSION

In the present study, the expressions of serum DKK-1 and sclerostin were independent of disease activity. Sclerostin was negatively correlated with the mSASSS, which suggests that sclerostin may be a potential marker indicating the spine ossification process in AS. The specific mechanism remains to be investigated.

Dickkopf-1: Current knowledge and related diseases

Dickkopf-1(DKK-1) has been identified as a secretory protein that can inhibit the Wnt signaling transduction pathway. It is well known that the Wnt signaling pathway plays an important role in embryogenesis, organogenesis and homeostasis. This signaling cascade is essential for many normal physiological processes such as cellular proliferation, tissue regeneration, embryonic development and many other systemic and local effects, and it can be regulated at different levels. Therefore, defects in the pathway may lead to some complicated effects. In addition, it has been demonstrated that defects in this pathway are closely linked to some diseases including cancer, rheumatism, bone disease, diabetes, and Alzheimer disease. Since DKK-1 is an antagonist of the Wnt pathway, it may be related to these diseases; in fact, many studies have identified this fact. This review will summarize the current knowledge of DKK-1 and DKK-1-mediated regulation of Wnt signaling in the development of these related diseases.

Parathyroid hormone is a determinant of serum Dickkopf-1 levels in ankylosing spondylitis

Available studies reported contradictory results about serum levels Dickkopf-1 (DKK1), an inhibitor of Wnt signaling in patients with ankylosing spondylitis (AS). In previous studies, we observed in other conditions that parathyroid hormone (PTH) serum levels were an important determinant of DKK1 serum levels. The aim of the present study was to investigate it in patients with AS. We recruited 71 patients diagnosed with AS. Levels of C-reactive protein (CRP), DKK1, PTH, 25OH-vitamin D, and bone turnover markers (intact N-propeptide of type I collagen, P1NP, and C-terminal telopeptide of type I collagen, CTX) were measured and compared to healthy controls (HC). Dual X-ray absorptiometry at lumbar spine and proximal femoral site was used for bone mineral density (BMD) assessment and spine X-rays were also performed. PTH serum levels were found to be significantly higher in AS patients than in HC (33.8 ± 14.11 vs 24.8 ± 13 pg/ml, p = 0.002), while mean DKK1 serum levels were lower than in HC (23.3 ± 13.1 vs 29.8 ± 15.9 pmol/l, p = 0.009). A positive correlation between DKK1 and PTH (correlation coefficient + 0.25, p = 0.03) was observed; it remained significant in a multivariate analysis. In patients with longer disease duration, DKK1 was also positively correlated with CTX (coefficient 0.42, p = 0.01), and PTH was higher in those patients with low BMD (Z-score ≤ - 1) at any site (p = 0.04). Also in AS, PTH is an important determinant of DKK1 serum levels and should be evaluated in studies on DKK1. PTH might have a role in bone involvement in AS, also through the Wnt pathway.

Role of IL-32 Gamma on Bone Metabolism in Autoimmune Arthritis

IL-32 acts as a pro-inflammatory cytokine by inducing the synthesis of inflammatory molecules as well as promoting the morphological changes involved in the transformation of monocytes into osteoclasts (OCs). Evaluation of the functions of IL-32 has mainly focused on its inflammatory properties, such as involvement in the pathogenesis of various autoimmune diseases. Recently, IL-32 was shown to be involved in bone metabolism, in which it promotes the differentiation and activation of OCs and plays a key role in bone resorption in inflammatory conditions. IL-32γ also regulates bone formation in conditions such as ankylosing spondylitis and osteoporosis. In this review, we summarize the results of recent studies on the role of IL-32γ in bone metabolism in inflammatory arthritis.

Bone Disease in Axial Spondyloarthritis

Axial spondyloarthritis is a chronic inflammatory skeletal disorder with an important burden of disease, affecting the spine and sacroiliac joints and typically presenting in young adults. Ankylosing spondylitis, diagnosed by the presence of structural changes to the skeleton, is the prototype of this disease group. Bone disease in axial spondyloarthritis is a complex phenomenon with the coexistence of bone loss and new bone formation, both contributing to the morbidity of the disease, in addition to pain caused by inflammation. The skeletal structural changes respectively lead to increased fracture risk and to permanent disability caused by ankylosis of the sacroiliac joints and the spine. The mechanism of this new bone formation leading to ankylosis is insufficiently known. The process appears to originate from entheses, specialized structures that provide a transition zone in which tendon and ligaments insert into the underlying bone. Growth factor signaling pathways such as bone morphogenetic proteins, Wnts, and Hedgehogs have been identified as molecular drivers of new bone formation, but the relationship between inflammation and activation of these pathways remains debated. Long-standing control of inflammation appears necessary to avoid ankylosis. Recent evidence and concepts suggest an important role for biomechanical factors in both the onset and progression of the disease. With regard to new bone formation, these processes can be understood as ectopic repair responses secondary to inflammation-induced bone loss and instability. In this review, we discuss the clinical implications of the skeletal changes as well as the underlying molecular mechanisms, the relation between inflammation and new bone formation, and the potential role of biomechanical stress.

Predisposition of six well-characterized microRNAs to syndesmophytes among Chinese patients with ankylosing spondylitis

OBJECTIVES

We quantified the expression of six well-characterized microRNAs (miRNAs) in peripheral blood mononuclear cells to see whether they can predispose to syndesmophytes in ankylosing spondylitis (AS) patients.

METHODS

This is a cross-sectional study involving 46 AS patients (23/23 with/without syndesmophytes) and 22 healthy controls. miRNAs expression was quantified by real-time PCR.

RESULTS

Six examined miRNAs were comparably expressed between AS patients without syndesmophytes and healthy controls (p > .05). Relative to AS patients without syndesmophytes, patients with syndesmophytes had significantly higher levels of miR-29a, miR-335-5p, miR-27a and let-7i (p = .001, .002, .013 and .029, respectively). Nine significant contributors associated with syndesmophytes in AS, including smoking, AS duration, human leukocyte antigen B27, erythrocyte sedimentation rate, C-reactive protein, miR-335-5p, miR-27a, miR-218 and sacroiliitis, were identified. The addition of miR-335-5p, miR-27a and miR-218 can significantly improve the accuracy of baseline risk factors. Based on the nine significant contributors, a nomogram was constructed, with good prediction accuracy (C-index: 0.86, p < .001).

CONCLUSION

We provide evidence for the predisposition of miR-335-5p, miR-27a and miR-218 to syndesmophytes in AS patients, indicating a contributory role of miRNAs in the pathogenesis of syndesmophytes. Further validation is warranted.